please answer these as soon as possible, thank you

2.10 Consider the advisor relation shown in Figure 2.8, with s_ id as the primary key of advisor. Suppose a student can have more than one advisor. Then, would s_id still be a primary key of the advisor relation? If not, what should the primary key of advisor be? 2.14 List two reasons why null values might be introduced into the database. Figure 2.8 Schema diagram for the university database